1. Field of the Invention
The present invention relates to an image forming apparatus which includes a pickup roller which transports a sheet placed on a paper feeding tray, and a pressing plate which applies a bias to the sheet to press on the pickup roller.
2. Description of the Related Art
An image forming apparatus which includes a roller supporting mechanism which supports a pickup roller to be movable vertically, an ascending mechanism which makes the pressing plate ascend toward the pickup roller, an a coupling member which moves in conjunction with a vertical movement of the pickup roller, a drive gear to which a driving force from a drive source is transmitted, and a transmission-state switching mechanism which is engaged with the coupling member, and which allows or inhibits the transmission of the driving force from the drive gear to the ascending mechanism according to the movement of the coupling member, has hitherto been known. In this technology, as the number of sheets in the paper feeding tray goes on decreasing, and the pickup roller descends, the movement of the pickup roller is transmitted to the transmission-state switching mechanism via the coupling member, and a state of transmission from the drive gear to the ascending mechanism is switched from an inhibited state to an allowed state.
Accordingly, the pressing plate ascends up, and the pickup roller is elevated by the pressing plate via the sheet, returning to an initial position. Therefore, due to the pickup roller positioned at the initial position, it is possible to transport a sheet once again in a favorable manner. In other words, in this technology, without providing a sensor which detects a decrease in the number of sheets, it is possible to move automatically a position of the pickup roller and a position of the pressing plate to appropriate positions, in accordance with the decrease in the number of sheets, by a mechanical structure.